It has been estimated that as many as 75% of newly produced B cells are autoreactive. Three complementary mechanisms prevent these autoreactive cells from causing autoimmunity; clonal deletion, receptor editing, and anergy. We have recently shown that up to 50% of immature B cells are destined to become anergic. Thus anergy may silence the majority of autoreactive B cells. Unlike clonal deletion and editing, which occur primarily in immature bone marrow B cells, anergy can occur in peripheral B cells and is reversible. Therefore, anergy may be particularly important physiologically for silencing autoreactive B cells generated in germinal centers by somatic mutation. Reversal or escape from anergy would allow such B cells to participate in autoimmunity. Until recently it has not been possible to study the frequency and/or biology of anergic cells in a physiologic (nontransgenic) setting. This has led to skepticism regarding the physiologic significance of anergy. We have recently defined a marker set that allows identification, isolation, and study of anergic B cells from a normal repertoire, and extension of our studies to humans. Using these tools we propose to address the hypothesis that anergic B cells arise by somatic mutation in germinal centers as well as from autoreactive germline specificities. We hypothesize that the high frequency production of autoreactive cells in humans dictates that a significant population of anergic B cells must exist in this species. We will address two specific questions. AIM 1: What are the origins of anergic B cells in wildtype mice? Proposed experiments will determine if there is a bias in the autoantibody specificities or affinities that are silenced by anergy in mice and quantitiate the frequency of cells bearing somatically mutated receptors in this population. AIM2: What markers define anergic B cells in humans? We will also determine the frequency of somatically mutated receptor in this population and the specificities and affinities of autoantibodies that lead to anergy in humans. Relevance: Autoantibodies are characteristic of many autoimmune diseases. Anergy is one mechanism by which B cells are prevented frombecoming effective antigen presenting cells and producing autoantibodies. This work will allow us to identify anergic cells in humans and further our understanding of the conditions which lead to B cell anergy. [unreadable] [unreadable]